The invention relates to a mineral-insulated electrical cable having a tubular casing and several metal conductors running within the tubular casing and projecting from it, which are insulated against one another and against the tubular casing, wherein the tubular casing has a gas-tight seal on at least one end, through which the conductors are passed, and wherein the conductors projecting out of the seal, in the connection with the seal and over a portion of their length, each have a sheath of at least one material selected from the group of ceramics, glass, and glass ceramics.
A so-called MI (mineral-insulated) cable of this type is known from German published patent application DE 195 09 132 A1. They are used, for example, for purposes of measurement and regulation in the sensor technology area in motor vehicles and are there exposed to relatively high temperatures, for example in the exhaust gas system. The MI cable has a casing which is made of a metal tube. The conductors run in an insulation of a mineral powder. A gas-tight glass seal is arranged at the outlet opening for the conductors from the metal tube. A ceramic molded part is pushed over the conductors projecting out of the metal tube. With such cables, there are typically corrosion phenomena in the outlet area of the conductors from the metal casing or in the seal or even in the molded part. These corrosion phenomena are caused by condensate formation between the (current-bearing) conductors. It is known to use corrosion-resistant cables of titanium or tantalum. These materials have a high corrosion resistance, but a relatively poor ductility and mechanical stability at high thermal alternating stress. Since the conductors of an MI cable are frequently contacted by clamping action, they must have good elastic properties. This is only the case to a very limited extent with titanium and tantalum. Also, neither material is optimally suited for a welding connection with further contact materials, for example on a sensor chip. The similarly used high grade steel cables do not, to be sure, have these disadvantages and are in addition very easily manufacturable, but are nonetheless very susceptible to corrosion with current flow.
An electrical cable having a tubular casing and several conductors running within the tubular casing and projecting out of them is known from German published patent application DE 27 17 765 A1. The conductors are insulated against each other and against the metal tubular casing by an insulation sleeve. The tubular casing is joined at one end with a connection element, wherein the juncture is closed off gas-tight with a seal. The so-described connection element serves for liquid-tight installation, for example of underwater cables.
A similar electrical cable is known from British patent specification GB 1 270 100. This is constructed as a mineral-insulated cable, wherein the individual conductors have a conventional insulation sleeve. The insulation sleeves serve for corrosion protection and are made of plastic.